With the 2018 midterms over, the political calendar instantly turned to 2020, when President Donald Trump is up for re-election.

The Democratic field threatens to be as unwieldy as the Republican race was in 2016. That's when Trump triumphed over 16 other GOP hopefuls.

There is no shortage of Democrats eyeing the 2020 contest, including U.S. Sen. Cory Booker, D-N.J., who was helped when the New Jersey Legislature voted to make it clear that he could run for both president and re-election two years from now.

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U.S. Sen. Cory Booker addresses students at the University of New Hampshire in October. (Jonathan D. Salant | NJ Advance Media for NJ.com)

Michael Bloomberg, the former mayor of New York City. (Jeff Kowalsky | Bloomberg)

9. Former New York Mayor Michael Bloomberg

The Democrat-turned-Republican-turned-independent is now a Democrat again and spent at least $38 million to help his new party in the midterms. That made him the third biggest spender in 2018, according to the Center for Responsive Politics.